1. Field of the Invention
The present invention relates to an ink jet printer and more particularly to an ink jet printer wherein ink is supplied to an ink tank disposed on a movable carriage from a main tank provided outside the movable carriage.
2. Description of the Prior Art
According to a known ink jet printer, a main tank is provided outside a movable carriage and ink is supplied (replenished) from the main tank to an ink tank disposed on the movable carriage.
For example, in Japanese Published Examined Patent Application No. Sho 54-31898 (hereinafter referred to as the xe2x80x9cprior art reference 1xe2x80x9d) there is disclosed a construction wherein a liquid reservoir filled with a liquid absorber is provided within a print head, and a wick provided in a liquid filling device is inserted into the liquid reservoir from a fill opening and is brought into contact with the liquid absorber, whereby ink is supplied to the liquid reservoir from the liquid filling device under the action of capillarity.
In Japanese Published Examined Patent Application No. Sho 60-9903 (xe2x80x9cprior art reference 2xe2x80x9d hereinafter) there is disclosed a construction wherein the amount of ink remaining in an ink tank disposed on a carriage is detected and if it is below a predetermined amount, the carriage is moved to a print stand-by position and ink is replenished to the ink tank by being dropped from a base tank provided at an upper position.
In Japanese Published Examined Patent Application No. Sho 63-51868 (xe2x80x9cprior art reference 3xe2x80x9d hereinafter) there is disclosed a construction wherein a sub-tank and a main tank both mounted on a carriage are connected together through a feed pipe and, when the ink in the sub-tank decreases, ink is fed under pressure into the sub-tank by pressing the main tank, while air present within the sub-tank is discharged through a discharge pipe into a bag-like container.
In Japanese Published Examined Patent Application No. Hei 7-51356 (xe2x80x9cprior art reference 4xe2x80x9d) there is disclosed a construction wherein a first tank disposed on a carriage and a second tank disposed outside the carriage are connected together through two connecting pipes and ink is fed under pressure from the second tank to the first tank through one of the connecting pipes, while an overflow is recovered into the second tank through the other.
Further, in Japanese Patent No. 2772014 (xe2x80x9cprior art reference 5xe2x80x9d hereinafter) there is disclosed a construction wherein, when a residual amount detecting electrode in a first ink tank disposed on a carriage detects reduction of the residual amount of ink, a mechanical valve in a tube which connects the first ink tank and a second ink tank disposed outside the carriage with each other is opened, whereby ink is replenished automatically from the second ink tank which is located at a higher position than the first ink tank.
The above conventional ink jet printers involve the following inconveniences.
In the prior art reference 1, a satisfactory ink shift cannot be done in some particular liquid distribution condition in the interior of the liquid reservoir, and the evaporation and denaturation of ink are apt to occur because the wick is exposed at all times.
In the prior art reference 2, the dropped ink adheres to a wall surface or the like and is denatured or solidified, which may obstruct printing.
In the prior art reference 3, the internal pressure of the sub-tank becomes a positive pressure because ink is fed to the sub-tank under pressure, and the positive pressure also acts on a print head orifice, causing the leakage of ink such as face-flood.
In the prior art reference 4, it is necessary that the first tank be disposed lower than a print head, and ink which has been increased in viscosity is pressurized so as to be discharged from the print head, so that ink is apt to leak from a connection.
In the prior art reference 5, there occurs ink leakage upon deterioration of the mechanical valve.
The present invention has been accomplished for eliminating the abovementioned inconveniences and provides an ink jet printer capable of preventing link leakage from a connection between a main tank disposed outside a carriage and an ink tank disposed on the carriage and thereby capable of ensuring a stable supply of ink.
According to the present invention, in one aspect thereof, there is provided an ink jet printer including an ink tank which is held on a movable carriage with a print head mounted thereon and in which ink is held so as to have a free surface, the ink tank having plural to-be-connected portions for the replenishment of ink; a main tank disposed outside the movable carriage and with the ink stored therein; a first connecting portion communicating with the main tank; a second connecting portion through which air is discharged to the exterior by means of an air suction part; and a connecting part which, at the time of ink supply, connects the first and second connecting portions respectively to the to-be-connected portions of the ink tank.
In the present invention, the supply of ink from the main tank disposed outside the movable carriage to the ink tank disposed on the movable carriage is performed in the following manner. First, the first and second connecting portions are connected respectively to the to-be-connected portions of the ink tank by the connecting part. Next, the air present in the interior of the ink tank is discharged to the exterior from the second connecting portion by the air suction part (e.g., a pump) to increase a negative pressure in the ink tank. As a result, ink is replenished from the main tank to the ink tank through the first connecting portion. Since the replenishment of ink is thus performed by suction of the ink from the main tank under the action of the negative pressure in the ink tank, there is no fear of ink leakage to the exterior from the connection between the first connecting portion and the corresponding to-be-connected portion of the ink tank.
In another aspect of the present invention, the ink tank is made up of a first ink chamber having an atmosphere communication port and with an ink holding capillary member accommodated therein, a second ink chamber which holds the ink so as to have a free surface, the second ink chamber having an ink supply port for the supply of ink to the print head and also having to-be-connected portions, and a meniscus forming member provided in a communicating portion between the first and second ink chambers, and the ink jet printer further includes a residual ink quantity detecting part which detects a residual ink quantity in the second ink chamber and a control part which, when the residual ink quantity is found to be below a predetermined quantity by the residual ink quantity detecting part, makes control to drive the connecting part so as to connect the first and second connecting portions respectively to the to-be-connected portions in the second ink chamber and also makes control to actuate the air suction part so as to replenish ink from the main tank to the ink tank.
In printing, the ink contained in the capillary member in the first ink chamber shifts to the second ink chamber by virtue of a negative pressure created by ejection of ink droplets from the print head. When the ink in the first ink chamber is used up, the ink present in the second ink chamber is consumed. In this case, bubbles break an ink meniscus film formed by the meniscus forming member and shift from the first to the second ink chamber to control the negative pressure in the second ink chamber to a level falling under a predetermined range, thereby maintaining the ejection of ink droplets from the print head in good condition. When the residual ink quantity is found to be below the predetermined quantity by the residual ink quantity detecting part, the ejection of ink droplets is stopped and the control part makes control to actuate the connecting part so as to connect the first and second connecting portions to the to-be-connected portions in the second ink chamber and also makes control to actuate the air suction part so as to discharge the air present in the second ink chamber and replenish ink from the main tank.
Thus, in normal printing, the negative pressure control on the print head side is performed with the ink tank alone independently, so the main tank can be installed freely with respect to the ink tank (print head) and the degree of freedom in components"" arrangement becomes higher.
In a further aspect of the present invention, the ink jet printer is further provided with a closing part which closes the atmosphere communication port in the first ink chamber at the time of replenishing ink from the main tank to the ink tank.
Thus, during the supply of ink from the main tank to the ink tank, the atmosphere communication port in the first ink chamber is closed by the closing part. Therefore, when the air present in the second ink chamber is discharged to the exterior by suction to increase the negative pressure in the second ink chamber, there is no fear that the negative pressure in the second ink chamber may be decreased by the entry of air into the second ink chamber from the first ink chamber having the atmosphere communication port. That is, ink can be supplied from the main tank to the ink tank efficiently.
In a still further aspect of the present invention, the to-be-connected portions of the ink tank and the first and second connecting portions are connected together when the movable carriage is in its home position thereof.
Since the ink tank and the connecting portions of the ink replenishing station are connected together upon return of the movable carriage to its home position after printing, it is not necessary to move the carriage in a main-scanning direction, which is efficient. Further, since the replenishment of ink is performed at the home position, the print head is capped into a hermetically sealed state, so that it is possible to prevent the entry of air into the print head at the time of replenishment of ink.
In a still further aspect of the present invention, the residual ink quantity detecting part is an optical sensor which detects an ink level on the basis of a change in light transmittance caused by whether ink is present or not.
The light transmittance differs depending on whether ink is present up to the position (height) where the optical sensor is installed in the ink tank. Therefore, it is possible to surely detect the ink level on the basis of the transmittance of light and ink can be replenished from the main tank to the ink tank at an appropriate timing.
In a still further aspect of the present invention, a defective ink detecting part which detects defective ink on the basis of the rate of attenuation of light passing through the ink is provided in the communication path between the main tank and the first connecting portion.
In the case where the attenuation rate of light detected by the defective ink detecting part is outside a predetermined range, it is judged that inappropriate ink is flowing from the main tank to the ink tank. In this case, for example the printing operation is stopped and the replacement of ink is instructed. Thus, it is possible to prevent the occurrence of any inconvenience in the print head caused by the flow of inappropriate ink.
In a still further aspect of the present invention, the main tank is provided with an atmosphere release port which is opened when the main tank is loaded into the ink jet printer.
After shipping of the main tank and until it is loaded into the ink jet printer, there is a fear that ink may leak to the exterior through the atmosphere release port due to vibrations or depending on in which direction the main tank is placed. In the present invention, however, such ink leakage can be prevented because the atmosphere release port is opened when the main tank is loaded into the ink jet printer.
In a still further aspect of the present invention, the to-be-connected portions are provided in an upper portion of the ink tank.
Since the to-be-connected portions are located in an upper portion of the ink tank, the supply of ink to the second ink chamber can be done from above the ink level and not into the ink (below the ink level). Consequently, the amount of ink adhered to the connecting portions decreases and the solidifying of adhered ink is suppressed. Connecting the first and second connecting portions to the to-be-connected portions and closing the atmosphere communication port can be completed in a single operation and thus it is possible to effect the ink supplying operation efficiently.